sk-unix: don't pass a negative value to close()

CID 190174 (#1 of 1): Argument cannot be negative (NEGATIVE_RETURNS)
6. negative_returns: fd is passed to a parameter that cannot be negative.
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

criu/sk-unix.c

@@ -217,7 +217,7 @@ int kerndat_socket_unix_file(void)
 		return 0;
 	}
 	close(sk);
-	close(fd);
+	close_safe(&fd);
 
 	kdat.sk_unix_file = true;